CN111880288A - Optical imaging system - Google Patents

Abstract

An optical imaging system includes a first lens group having a first group of lenses. The most anterior lens of the first group of lenses is the lens closest to the object and has a positive refractive power. The optical imaging system further includes a second lens group having a second group of lenses. The rearmost lens of the second group of lenses is the lens closest to the image plane and has a convex surface. The first lens group and the second lens group are sequentially disposed from an object side to an imaging surface. An expression TL/f1<2.0 is satisfied, where TL denotes a distance on the optical axis from the object side surface of the frontmost lens to the imaging plane, and f1 denotes a focal length of the frontmost lens.

Description

Optical imaging system

The application is a divisional application of an invention patent application with application date of 2017, month 5 and 18, priority date of 2016,month 12 and 20, application number of 201710351472.5 and invention name of "optical imaging system".

Technical Field

The present disclosure relates to a telescopic optical imaging system (telestratic imaging system) including five or more lenses.

Background

A telescopic optical system capable of capturing an image of an object at a long distance may have a large size. For example, the ratio (TL/f) of the Total Length (TL) of the telescopic optical system to the total focal length (f) of the telescopic optical system may be 1 or more. Therefore, it may be difficult to mount such a telescopic optical system in a small electronic product such as a mobile communication terminal.

Disclosure of Invention

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

According to an aspect of the present disclosure, an optical imaging system includes a first lens group having a first group of lenses, wherein a most anterior lens of the first group of lenses is a lens closest to an object and has a positive refractive power. The optical imaging system further comprises a second lens group having a second group of lenses, wherein a rearmost lens of the second group of lenses is a lens closest to an imaging surface and has a convex surface. The first lens group and the second lens group are sequentially disposed from an object side to an imaging surface. An expression TL/f1<2.0 is satisfied, where TL denotes a distance from an object side surface of the frontmost lens to an image plane, and f1 denotes a focal length of the frontmost lens.

The optical imaging system may include a lens having a forwardmost edge with a convex object side surface. The optical imaging system may include another lens disposed adjacent to an image side surface of the most anterior lens, wherein the other lens has a negative refractive power. The optical imaging system may include a rearmost lens having a refractive index higher than 1.6 and less than 1.75.

The optical imaging system may satisfy the conditional expression 0.9mm (millimeter) < d1G2G <1.7mm, where d1G2G denotes a distance from an image side surface of a lens closest to an imaging surface among lenses of the first lens group to an object side surface of a lens closest to an object side among lenses of the second lens group. The optical imaging system may satisfy the conditional expression-1.0 < f1G/f2G < -0.2, where f1G denotes a combined focal length of the first lens group, and f2G denotes a combined focal length of the second lens group. The optical imaging system may satisfy the conditional expression 0.3< tan θ <0.5, where θ represents a half of a field angle of the optical imaging system.

The optical imaging system may include a first lens group composed of a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a negative refractive power. The third lens of the optical imaging system may comprise a convex object side surface. The optical imaging system may further include a second lens group composed of a fourth lens having a negative refractive power and a fifth lens having a positive refractive power. The fourth lens of the optical imaging system may comprise a concave object side surface.

Alternatively, the optical imaging system may also include a first lens group composed of a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a negative refractive power, and a fourth lens having a positive refractive power. Optionally, the optical imaging system may further include a second lens group composed of a fifth lens having a negative refractive power and a sixth lens having a positive refractive power.

In another general aspect, an optical imaging system includes: a first lens having a positive refractive power; a second lens having a negative refractive power; a third lens having a negative refractive power; a fourth lens having a negative refractive power; and a fifth lens having a positive refractive power. The first lens to the fifth lens are sequentially disposed from an object side to an image plane. The optical imaging system satisfies the conditional expression 0.7< TL/f <1.0, where TL denotes a distance on an optical axis from an object side surface of the first lens to an imaging plane, and f denotes a total focal length of the optical imaging system.

The optical imaging system may further satisfy the conditional expression-2.5 < f/f2< -0.5, where f denotes an overall focal length of the optical imaging system, and f2 denotes a focal length of the second lens. The optical imaging system may satisfy the conditional expression-3.5 < f/f3< -0.4, where f denotes an overall focal length of the optical imaging system, and f3 denotes a focal length of the third lens.

In another general aspect, an optical imaging system includes: a first lens having a convex object-side surface along an optical axis; a second lens having a convex object side surface and a concave image side surface along an optical axis; a third lens having a concave image side surface along an optical axis; a fourth lens having a concave object side surface and a concave image side surface along an optical axis; and a fifth lens having a convex object side surface and a convex image side surface along an optical axis.

The optical imaging system may have a first lens with a concave image side surface and a third lens with a concave object side surface. The optical imaging system can have a first lens with a convex image side surface and a third lens with a convex object side surface.

Drawings

The above and other aspects, features and advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

fig. 1 is a diagram showing an optical imaging system according to a first example;

FIG. 2 is a set of graphs representing aberration curves of the optical imaging system shown in FIG. 1;

FIG. 3 is a table listing aspheric characteristics of the optical imaging system shown in FIG. 1;

fig. 4 is a diagram showing an optical imaging system according to a second example;

FIG. 5 is a set of graphs representing aberration curves of the optical imaging system shown in FIG. 4;

FIG. 6 is a table listing aspheric characteristics of the optical imaging system shown in FIG. 4;

fig. 7 is a diagram showing an optical imaging system according to a third example;

FIG. 8 is a set of graphs representing aberration curves for the optical imaging system shown in FIG. 7;

FIG. 9 is a table listing aspheric characteristics of the optical imaging system shown in FIG. 7;

fig. 10 is a rear view illustrating a mobile communication terminal mounted with an optical imaging system according to an embodiment of the present disclosure;

fig. 11 is a sectional view taken along line I-I' showing the mobile communication terminal shown in fig. 10.

Detailed Description

Hereinafter, embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. The following detailed description is provided to assist the reader in obtaining a thorough understanding of the methods, devices, and/or systems described herein. However, various alternatives, modifications, and equivalents of the methods, apparatus, and/or systems described herein will be apparent to those skilled in the art in view of the disclosure of the present application. For example, the order of operations described herein is merely an example, and is not limited to the order set forth herein, as variations may be made in addition to the operations which must occur in a particular order, which will be apparent upon understanding the disclosure of the present application. Further, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

The features described herein may be embodied in different forms and should not be construed as limited to the examples described herein. Rather, the examples described herein are provided merely to illustrate some of the many possible ways to implement the methods, devices, and/or systems described herein that will be apparent upon understanding the disclosure of the present application.

Although terms such as "first," "second," and "third" may be used herein to describe various components, regions, or sections, these components, regions, or sections are not limited by these terms. Rather, these terms are only used to distinguish one component, region or section from another component, region or section. Thus, a first component, region or section referred to in an example described herein can also be referred to as a second component, region or section without departing from the teachings of the example.

The terminology used herein is for the purpose of describing various examples only and is not intended to be limiting of the disclosure. The singular is intended to include the plural unless the context clearly dictates otherwise. The terms "comprising," "including," and "having" specify the presence of stated features, integers, operations, elements, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, operations, components, elements, and/or groups thereof.

Variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, may occur. Thus, the examples described herein are not limited to the particular shapes shown in the drawings, but include variations in shapes that occur during manufacture.

As will be apparent after understanding the disclosure of the present application, the features of the examples described herein may be combined in various ways. Further, while the examples described herein have various configurations, other configurations are possible, as will be apparent after understanding the disclosure of the present application.

According to an example, the first lens refers to the lens closest to the object or subject for which the image is captured. The fifth lens or the sixth lens is a lens closest to the imaging surface or the image sensor. In an embodiment, the radius of curvature of the lens, the thickness, the distance on the Optical Axis (OAL) from the object side surface of the first lens to the imaging plane, half the diagonal length of the imaging plane (IMGHT), and the focal length of each lens are all expressed in millimeters (mm). One skilled in the relevant art will appreciate that other units of measure may be used. Further, in the embodiment, the distance on the optical axis (SL) between the diaphragm and the image sensor, the image height (IMGHT), the Back Focal Length (BFL) of the lens, and the total focal length of the optical system are all expressed in millimeters (mm). In addition, the thickness of the lenses, the interval between the lenses, OAL, TL, and SL are distances measured based on the optical axes of the lenses.

The surface of the lens is convex means that the optical axis portion of the corresponding surface is convex, and the surface of the lens is concave means that the optical axis portion of the corresponding surface is concave. Therefore, in a configuration in which one surface of the lens is described as a convex surface, an edge portion of the one surface of the lens may be recessed. Similarly, in a configuration in which one surface of the lens is described as concave, an edge portion of the one surface of the lens may be convex. In other words, the paraxial region of the lens may be convex, while the remainder of the lens outside the paraxial region may be convex, concave, or flat. In addition, the paraxial region of the lens can be concave, while the remainder of the lens outside the paraxial region can be convex, concave, or flat. Further, in the embodiment, the thickness and the radius of curvature of the lens are measured with respect to the optical axis of the corresponding lens.

According to an illustrative example, an embodiment describing an optical system comprises five or six lenses having optical power. However, the number of lenses of the optical system may be changed, for example, between two to six lenses, while achieving various results and effects described below. Further, although each lens is described as having a particular optical power, at least one of the lenses may employ a different optical power to achieve the intended result.

The present disclosure provides an optical imaging system capable of capturing an image of a subject at a long distance and installed in a small-sized terminal. The optical imaging system may include two lens groups. For example, an optical imaging system includes a first lens group and a second lens group.

The first lens group includes a plurality of lenses. In an embodiment, the first lens group includes three or four lenses.

In an embodiment of the former case, the first lens group includes: a first lens having a positive refractive power; a second lens having a negative refractive power; and a third lens having a negative refractive power. The object side surface of the first lens is convex, the object side surface of the second lens is convex, and the image side surface of the second lens is concave. The image side surface of the third lens is concave.

In an embodiment of the latter case, the first lens group includes: a first lens having a positive refractive power; a second lens having a negative refractive power; a third lens having a negative refractive power; and a fourth lens having a positive refractive power. The object side surface of the first lens is convex. The object side surface of the second lens is convex and the image side surface of the second lens is concave. Both surfaces of the third lens are concave and both surfaces of the fourth lens are convex.

The first lens group includes an aspherical lens. For example, at least one surface of all lenses constituting the first lens group is an aspherical surface. The first lens group may include a plastic lens. As an example, all lenses constituting the first lens group are formed of plastic.

The second lens group includes a plurality of lenses. In an embodiment, the second lens group includes a lens having a negative refractive power and a lens having a positive refractive power. Here, both surfaces of the lens having a negative refractive power are concave surfaces, and both surfaces of the lens having a positive refractive power are convex surfaces.

The second lens group includes an aspherical lens. For example, at least one surface of all lenses constituting the second lens group is an aspherical surface. The second lens group may include a plastic lens. As an example, all lenses constituting the second lens group are formed of plastic.

In the optical imaging system, the aspherical surface of each lens may be represented by the following equation 1:

[ equation 1]

Here, c denotes an inverse of a curvature radius of the lens, k denotes a conic constant, r denotes a distance from a certain point on an aspherical surface of the lens to an optical axis, a to H and J denote aspherical coefficients, and Z (or SAG) denotes a distance between the certain point on the aspherical surface of the lens at a distance r from the optical axis and a tangent plane tangent to a vertex of the aspherical surface of the lens.

The optical imaging system further includes a filter, an image sensor, and a diaphragm. The optical filter is disposed between the rearmost lens of the second lens group and the image sensor. The filter blocks part of the wavelength of light so that a clear image can be realized. For example, the optical filter is configured to filter out light in the infrared wavelength.

The image sensor may form an imaging plane. For example, the surface of the image sensor forms an imaging plane. To adjust the amount of light incident on the lens, a diaphragm may be provided. For example, the stop is disposed between the second lens and the third lens.

The optical imaging system may satisfy any one of the following conditional expressions or any combination of any two or more of the following conditional expressions:

[ conditional expression 1]0.7< TL/f <1.0

[ conditional expression 2]0.9< d1G2G <1.7

[ conditional expression 3] -2.5< f/f2< -0.5 [ ]

[ conditional expression 4] -3.5< f/f3< -0.4 [ ]

[ conditional expression 5]1.6< Ndi <1.75

[ conditional expression 6]0.3< tan theta <0.5

[ conditional expression 7] -1.0< f1G/f2G < -0.2 [ ]

[ conditional expression 8] TL/f1<2.0.

Here, TL denotes a distance on the optical axis from the object side surface of the first lens to the imaging surface, f denotes a total focal length provided for optical imaging, d1G2G denotes a distance on the optical axis from the image side surface of a lens closest to the imaging surface among the lenses of the first lens group to the object side surface of a lens closest to the object side among the lenses of the second lens group, f2 denotes a focal length of the second lens, f3 denotes a focal length of the third lens, Ndi denotes a refractive index of the lens closest to the imaging surface, θ denotes a half of an angle of view of the optical imaging system, f1G denotes a composite focal length of the first lens group, f2G denotes a composite focal length of the second lens group, and f1 denotes a focal length of the most anterior lens (first lens).

Conditional expression 1 is a parameter ratio for downsizing the optical imaging system. For example, in the case where TL/f exceeds the upper limit value ofconditional expression 1, it may be difficult to miniaturize the optical imaging system, so that it may be difficult to install the optical imaging system in a mobile communication terminal. In the case where TL/f is less than the lower limit value ofconditional expression 1, it may be difficult to manufacture the optical imaging system.

Conditional expression 2 is a parameter for realizing a telescopic optical system. For example, in the case where d1G2G is lower than the lower limit value ofconditional expression 2, the focal length of the optical imaging system may be short, making it difficult to mount the optical imaging system in the telephoto camera module. In the case where d1G2G exceeds the upper limit value ofconditional expression 2, the Total Length (TL) of the optical imaging system may be long, making it difficult to sufficiently miniaturize the optical imaging system.

Conditional expression 3 is a parameter ratio relating to the second lens to realize a high-resolution optical imaging system. For example, in the case where f/f2 is out of the numerical range ofconditional expression 3, the second lens may increase astigmatism of the optical imaging system, resulting in deterioration of an image.

Conditional expression 4 is a parameter ratio for the third lens to realize a high-resolution optical imaging system. For example, in the case where f/f3 is out of the numerical range ofconditional expression 4, the third lens may increase astigmatism of the optical imaging system, resulting in deterioration of an image.

Conditional expression 5 is a parameter of the lens closest to the imaging plane to realize a high-resolution optical imaging system. For example, in the case where Ndi satisfies the numerical range of conditional expression 5, the lens closest to the imaging plane may have a low abbe number of 26 or less, which is advantageous for correction of astigmatism, longitudinal chromatic aberration, and magnification aberration.

Conditional expression 6 represents a range for realizing the angle of field of the telescopic optical imaging system.Conditional expression 7 represents an appropriate focal length ratio between the first lens group (for correcting aberration of the optical imaging system) and the second lens group (for correcting curvature of the imaging surface).

Next, an optical imaging system according to several embodiments will be described. First, an optical imaging system according to a first embodiment will be described with reference to fig. 1. Theoptical imaging system 100 includes afirst lens group 1G and asecond lens group 2G.

Thefirst lens group 1G includes afirst lens 110, asecond lens 120, and athird lens 130. Thefirst lens 110 has a positive refractive power. Both surfaces of thefirst lens 110 are convex surfaces. Thesecond lens 120 has a negative refractive power. The object side surface of thesecond lens 120 is convex, and the image side surface of thesecond lens 120 is concave. Thethird lens 130 has a negative refractive power. The object side surface of thethird lens 130 is convex, and the image side surface of thethird lens 130 is concave.

Thesecond lens group 2G includes afourth lens 140 and afifth lens 150. Thefourth lens 140 has a negative refractive power. Both surfaces of thefourth lens 140 are concave. Further, an inflection point is formed on the image side surface of thefourth lens 140. For example, the image side surface of thefourth lens 140 is concave near the optical axis and convex at the edge. Thefifth lens 150 has a positive refractive power. Both surfaces of thefifth lens 150 are convex surfaces. Further, an inflection point is formed on the object side surface of thefifth lens 150.

Theoptical imaging system 100 further includes anoptical filter 170, animage sensor 180, and a diaphragm ST. Thefilter 170 is disposed between thefifth lens 150 and theimage sensor 180. The stop ST is disposed between thesecond lens 120 and thethird lens 130.

The optical imaging system configured as described above exhibits aberration characteristics as shown in the graph in fig. 2. Fig. 3 is a table listing aspherical characteristics of theoptical imaging system 100 according to the embodiment. The characteristics of the lens of theoptical imaging system 100 are listed in table 1.

[ Table 1]

An optical imaging system according to a second embodiment will be described with reference to fig. 4. Theoptical imaging system 200 includes afirst lens group 1G and asecond lens group 2G.

Thefirst lens group 1G includes afirst lens 210, asecond lens 220, and athird lens 230. Thefirst lens 210 has a positive refractive power. The object side surface of thefirst lens 210 is convex, and the image side surface of thefirst lens 210 is concave. Thesecond lens 220 has a negative refractive power. The object side surface of thesecond lens 220 is convex, and the image side surface of thesecond lens 220 is concave. Thethird lens 230 has a negative refractive power. Both surfaces of thethird lens 230 are concave.

Thesecond lens group 2G includes afourth lens 240 and afifth lens 250. Thefourth lens 240 has a negative refractive power. Both surfaces of thefourth lens 240 are concave. Further, an inflection point is formed on the image side surface of thefourth lens 240. For example, the image side surface of thefourth lens 240 is concave near the optical axis and convex at the edge. Thefifth lens 250 has a positive refractive power. Both surfaces of thefifth lens 250 are convex surfaces. Further, an inflection point is formed on the object side surface of thefifth lens 250.

Theoptical imaging system 200 further includes afilter 270, animage sensor 280, and a diaphragm ST. Thefilter 270 is disposed between thefifth lens 250 and theimage sensor 280. The stop ST is disposed between thesecond lens 220 and thethird lens 230.

The optical imaging system configured as described above exhibits aberration characteristics as shown in the graph in fig. 5. Fig. 6 is a table listing aspherical characteristics of the optical imaging system according to the embodiment. The characteristics of the lens of theoptical imaging system 200 are listed in table 2.

[ Table 2]

An optical imaging system according to a third embodiment will be described with reference to fig. 7. Theoptical imaging system 300 includes afirst lens group 1G and asecond lens group 2G.

Thefirst lens group 1G includes afirst lens 310, asecond lens 320, athird lens 330, and afourth lens 340. Thefirst lens 310 has a positive refractive power. The object side surface of thefirst lens 310 is convex, and the image side surface of thefirst lens 310 is concave. Thesecond lens 320 has a negative refractive power. The object side surface of thesecond lens 320 is convex, and the image side surface of thesecond lens 320 is concave. Thethird lens 330 has a negative refractive power. Both surfaces of thethird lens 330 are concave. Thefourth lens 340 has a positive refractive power. Both surfaces of thefourth lens 340 are convex surfaces.

Thesecond lens group 2G includes afifth lens 350 and asixth lens 360. Thefifth lens 350 has a negative refractive power. Both surfaces of thefifth lens 350 are concave. Further, an inflection point is formed on the image side surface of thefifth lens 350. For example, the image side surface of thefifth lens 350 is concave near the optical axis and convex at the edge. Thesixth lens 360 has a positive refractive power. Both surfaces of thesixth lens 360 are convex surfaces. Further, an inflection point is formed on the object side surface of thesixth lens 360.

Theoptical imaging system 300 further includes afilter 370, animage sensor 380, and a diaphragm ST. Thefilter 370 is disposed between thesixth lens 360 and theimage sensor 380. The stop ST is disposed between thesecond lens 320 and thethird lens 330.

The optical imaging system configured as described above exhibits aberration characteristics as shown in the graph in fig. 8. Fig. 9 is a table listing aspherical characteristics of the optical imaging system according to the embodiment. The characteristics of the lens of theoptical imaging system 300 are listed in table 3.

[ Table 3]

Table 4 shows values of conditional expressions of the optical imaging systems according to the first to third embodiments.

[ Table 4]

Next, a mobile communication terminal mounted with an optical imaging system according to an embodiment of the present disclosure will be described with reference to fig. 10 to 11.

Themobile communication terminal 10 includes a plurality ofcamera modules 20 and 30. Thefirst camera module 20 includes a firstoptical imaging system 101 configured to capture an image of a subject at a short-distance position, and thesecond camera module 30 includes a secondoptical imaging system 100, 200, or 300 configured to capture an image of a subject located at a long-distance position.

The firstoptical imaging system 101 includes a plurality of lenses. For example, the firstoptical imaging system 101 includes four or more lenses. The firstoptical imaging system 101 as a whole is configured to capture an image of an object located at a short distance position. As an example, the firstoptical imaging system 101 has a wide angle of field of 50 degrees or more, and a ratio (TL/f) of a Total Length (TL) of the firstoptical imaging system 101 to a total focal length (f) of the first optical imaging system is 1.0 or more.

The secondoptical imaging system 100, 200, or 300 includes a plurality of lenses. For example, the secondoptical imaging system 100, 200, or 300 includes six lenses. The secondoptical imaging system 100, 200, or 300 is any one of the optical imaging systems according to the first to third embodiments described above. The secondoptical imaging system 100, 200 or 300 is configured to capture an image of an object located at a distant location. As an example, the secondoptical imaging system 100, 200, or 300 has a field angle of 50 degrees or less, and a ratio (TL/f) of a Total Length (TL) of the second optical imaging system to a total focal length (f) of the second optical imaging system is less than 1.0.

The firstoptical imaging system 101 and the secondoptical imaging system 100, 200, or 300 may have substantially the same size. In an embodiment, the overall length L1 of the firstoptical imaging system 101 is substantially the same as the overall length L2 of the secondoptical imaging system 100, 200, or 300. Alternatively, in another embodiment, the ratio of the total length L1 of the firstoptical imaging system 101 to the total length L2 of the secondoptical imaging system 100, 200, or 300 (L1/L2) may be 0.8 to 1.0. In yet another alternative embodiment, the ratio of the total length L2 of the secondoptical imaging system 100, 200, or 300 to the thickness h of the mobile communication terminal 10 (L2/h) may be 0.8 or less.

As set forth above, according to the embodiments of the present disclosure, an optical imaging system capable of capturing an image of a subject located at a distant position and installed in a small-sized terminal can be realized.

While embodiments have been shown and described above, it will be apparent after understanding the disclosure of the present application that modifications or variations may be made without departing from the scope of the application as defined by the claims.

Claims (16)

1. An optical imaging system comprising:

a first lens group including a first group of lenses, wherein a most anterior lens of the first group of lenses is a lens closest to an object side and has a positive refractive power; and

a second lens group including a second group of lenses, wherein a rearmost lens of the second group of lenses is a lens closest to an image plane and has a convex surface,

wherein the first lens group and the second lens group are sequentially disposed from an object side to an imaging surface, and

wherein an expression TL/f1<2.0 is satisfied, where TL denotes a distance on the optical axis from the object side surface of the frontmost lens to the imaging plane, and f1 denotes a focal length of the frontmost lens.

2. The optical imaging system of claim 1, wherein the object side surface of the front most lens is convex.

3. The optical imaging system of claim 1, wherein a lens disposed adjacent to an image side surface of the forwardmost lens has a negative refractive power.

4. The optical imaging system of claim 1, wherein the rearmost lens has a refractive index higher than 1.6 and less than 1.75.

5. The optical imaging system according to claim 1, wherein an expression of 0.9mm < d1G2G <1.7mm is satisfied, wherein d1G2G denotes a distance on an optical axis from an image side surface of a lens closest to an imaging surface among the lenses of the first lens group to an object side surface of a lens closest to an object side among the lenses of the second lens group.

6. The optical imaging system according to claim 1, wherein an expression of-1.0 < f1G/f2G < -0.2 is satisfied, where f1G denotes a combined focal length of the first lens group, and f2G denotes a combined focal length of the second lens group.

7. The optical imaging system according to claim 1, wherein expression 0.3< tan θ <0.5 is satisfied, where θ represents a half of a field angle of the optical imaging system.

8. The optical imaging system of claim 1, wherein the first lens group comprises:

a first lens having a positive refractive power;

a second lens having a negative refractive power; and

and a third lens having a negative refractive power.

9. The optical imaging system of claim 8, wherein the object side surface of the third lens is convex.

10. The optical imaging system of claim 8, wherein the second lens group comprises:

a fourth lens having a negative refractive power; and

and a fifth lens having a positive refractive power.

11. The optical imaging system of claim 10, wherein the object side surface of the fourth lens is concave.

12. The optical imaging system of claim 1, wherein the first lens group comprises:

a first lens having a positive refractive power;

a second lens having a negative refractive power;

a third lens having a negative refractive power; and

and a fourth lens having a positive refractive power.

13. The optical imaging system of claim 12, wherein the second lens group comprises:

a fifth lens having a negative refractive power; and

and a sixth lens having a positive refractive power.

14. An optical imaging system comprising:

a first lens having a positive refractive power;

a second lens having a negative refractive power;

a third lens having a negative refractive power;

a fourth lens having a negative refractive power; and

a fifth lens having a positive refractive power,

wherein the first lens to the fifth lens are sequentially disposed from an object side to an image plane, and

wherein an expression 0.7< TL/f <1.0 is satisfied, where TL denotes a distance on an optical axis from an object side surface of the first lens to the imaging plane, and f denotes a total focal length of the optical imaging system.

15. The optical imaging system of claim 14, wherein the expression-2.5 < f/f2< -0.5 is satisfied, where f denotes an overall focal length of the optical imaging system, and f2 denotes a focal length of the second lens.

16. The optical imaging system of claim 14, wherein the expression-3.5 < f/f3< -0.4 is satisfied, where f denotes an overall focal length of the optical imaging system, and f3 denotes a focal length of the third lens.

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